Electrochemical cells, such as alkaline cells having a positive electrode including a metal oxide such as silver oxide, are commonly used as electrical energy sources. The battery is a primary power source for many portable electronic devices such as cameras, radios, toys, games, hearing aids, medical apparatus, such as insulin pumps, watches, printers, calculators, and the like.
Cells containing a metal oxide are usually noted for good voltage stability during discharge. It has been found, however, that during storage, especially at high temperatures, separator layers, such as cellulosic materials can be attacked and degraded or destroyed, for example, by the metal ions such as silver ions from the positive electrode that migrate to the separator as well as to the negative electrode where the silver ions can be reduced by the active materials and deposited on the surface thereof as metallic particles. The negative electrode can be oxidized and thereby undergo self-discharge which can reduce total capacity of the cell. To combat degradation of the separator, one construction that has been utilized was a multi-layer degradation resistant separator such as polyethylene and cellophane. However, such separators can be relatively expensive and further can have a volume which reduces the amount of active materials that can be contained in the cell.
Positive electrodes, including various layered or composite materials, have been disclosed in the art.
U.S. Pat. No. 3,630,780 relates to silver oxide electrodes for electric batteries, particularly primary batteries reportedly capable of delivering a high temporary current output, produced by compressing a mixture of 10 to 40 percent by weight of pulverulent silver oxide and 60 to 90 percent of pulverulent nickel, and hard-pressing the resulting compressed layer onto a carrier structure, preferably of copper or silver, at pressures of about 0.5 to about 1.4 t/cm.2 in an oxidizing or inert atmosphere at a hot-pressing temperature below the dissociation temperature of the silver oxide, this temperature being generally between about 100° C. and about 300° C.
U.S. Pat. No. 4,038,467 relates to a galvanic cell with negative zinc electrode and positive electrode of AgO, the AgO is surface-reduced to Ag2O, and insulated from the current takeoff, to which connection is made only by a porous silver layer.
U.S. Pat. No. 4,172,183 relates to an alkaline primary cell comprising a positive electrode having an upper layer, facing the negative electrode, of electrolytic γ-manganese dioxide to which 6-16% of graphite powder having a broad grain-size range has been added as a conducting additive. Disposed beneath this upper layer is at least one further layer containing γ-manganese dioxide, mercuric oxide, or monovalent silver oxide having a higher apparent specific gravity than the upper layer. A separator comprising at least one membrane layer is situated above the positive electrode.
U.S. Patent Application Publication No. 2005/0058903 relates to a battery that includes a cathode having an oxide containing one or more metals and pentavalent bismuth, an anode, a separator between the cathode and the anode, and an alkaline electrolyte. The metal(s) can be an alkali metal, an alkaline earth metal, a transition metal, and/or a main group metal. The separator reportedly can be ion-selective or capable of substantially preventing soluble bismuth ionic species from diffusing from the cathode to the anode.
Japanese Laid-Open Publication No. 56-06378 relates to reportedly improving the discharge rate and storability of a cell, by using a member comprising a porous nickel material of a three-dimensional network and porous material of silver or the like and having a specific structure, as a current collector between a positive electrode mainly composed of divalent silver oxide and a positive electrode case.
Japanese Laid-Open Publication No. 56-015561 relates to obtaining a battery reportedly with a long maintenance of high discharge-voltage and of a low cost by mixing graphite with nickel oxyhydroxide as a substitute for silver oxide.
Japanese Laid-Open Publication No. 58-163151 relates to reportedly improving the heavy load electric discharge characteristic by constituting the positive electrode black mix from an applied layer made of manganese dioxide on graphite which is formed on the surface of silver oxide in granular form.